Method of producing effusion holes

ABSTRACT

A method of producing a plurality of effusion holes in a wall of a combustor of a gas turbine engine comprises: determining a hole pattern definition which provides a functional relationship of the spacing between each adjacent hole within the row of holes; using the hole pattern definition to identify individual positions of the effusion holes to be produced; and using a hole producing system to produce the effusion holes at the identified positions.

TECHNICAL FIELD

The invention relates generally to gas turbine engines and, morespecifically, to a method of forming effusion holes in a combustor of agas turbine engine.

BACKGROUND OF THE ART

Cooling of combustor walls is typically achieved by directing coolingair through holes in the combustor walls to provide effusion and/or filmcooling. Holes formed in a predetermined pattern directly through asheet metal liner of the combustor walls allowing pressurized coolingair to enter the combustion chamber and thereby cool the combustor.

The effusion holes in the combustor walls are typically produced using alaser drilling system. During laser drilling, a laser head and aworkpiece are typically moved relative to the each other on amanipulation system such as a computer numerical control (CNC) motionsystem in order to drill each individual hole. In order to achieveoptimum cooling within the combustor, a non-uniform hole pattern isoften required. Accordingly, a hole pattern designed for optimumeffectiveness may comprise variations in hole density, which results ina hole pattern definition that is often complex. This in tarn requires asignificant amount of time to set up the laser drilling system, aspositional data for each individual hole must be defined and supplied tothe CNC motion system.

Current methods of defining complex hole patterns require that thedrilling of the effusion holes be done in two stages, wherein a coarserbase hole pattern is first drilled, and then, one or more finely-spacedholes are drilled between the base holes to define areas with a higherhole density where additional cooling is required. This requiresunnecessary and time-consuming repositioning moves by the laser drillingsystem which add to the cost of manufacturing the parts. There is thus aneed for an improved method of drilling the effusion holes whichminimizes manufacturing costs of effusion cooled parts.

SUMMARY

Accordingly, it is an object of the present invention to provide amethod of producing effusion holes which addresses the above mentionedconcerns.

According to one aspect there is provided a method of producing aplurality of effusion holes in a wall of a combustor of a gas turbineengine, the method comprising the steps of: a) determining a holepattern definition using: a count of the holes to be separated by firstspaces is a row of holes along a first axis, positional information of afirst hole in the row of holes, a first length of the row of holes, and,a first spacing ratio relating hole spacing distances between eachadjacent hole within the row of holes; b) using the hole patterndefinition to identify individual positions of fee effusion holes to beproduced in the wall of the combustor; and c) using a hole producingsystem to produce the effusion holes in the wall of the combustor at theidentified positions.

According to another aspect, there is provided a method of determiningindividual positions of effusion holes in a wall of a combustor of a gasturbine engine, the method comprising the steps of: a) using a geometricrelation that relates relative spacing distances between each of theeffusion holes separated by spaces in a row of holes to each other, thegeometric relation being L₁=aL₂=a²L₃=a^(n-1)L_(n)=(SR)L_(n), where L₁ isa first spacing distance, ‘a’ is a constant, ‘n’ if is a count of thespaces in the row of holes, L_(n) is a spacing distance associated witha space number n, and, ‘SR’ is a spacing ratio which is equal to a^(n-1)and provides a functional relationship between spacing distances of anyadjacent hole within the row of holes; and b) using positionalinformation of a first hole in the row of holes, a count of the holesand a length of the row of holes to determine the position of any of theeffusion holes within the row of holes in accordance with the geometricrelation.

There is further provided, in accordance with another aspect, a systemfor producing a plurality of spaced holes in a component, the systemcomprising: a hole producing machine; a control system, in communicationwith the hole producing machine; a hole pattern definition module whichprovides instructions to the control system for operating andcontrolling the hole producing, machine, the hole pattern definitionmodule determining a desired distribution of the effusion holes in thecomponent using predetermined input parameters, the distribution ofeffusion holes being, determined in accordance with the geometricrelation L₁=aL₂=a²L₃=a³L₄=a^(n-1)L_(n)=(SR)L_(n), where L₁ is a firstspacing distance, a is a constant, n is a count of the spaces in a rowof holes, L_(n) is a spacing distance associated with a space number n,and, SR is the first spacing ratio which is equal to a^(n-1); thepredetermined input parameters including: a count of the holes to beseparated by spaces in the row of holes along a first axis; positionalinformation of a first hole in the row of holes; a first length of therow of holes; and a first spacing ratio SR relating spacing distancesbetween each adjacent hole within the row of holes.

Further details of these and other aspects of the present invention willbe apparent from the detailed description and figures included below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1 is a schematic axial cross-section view of a gas turbine engine;

FIG. 2 is a partial side view of a combustor wall having a pattern ofeffusion holes drilled therein; and

FIG. 3 is a graphical representation of possible hole patterndefinitions according with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, amultistage compressor 14 for pressurizing the air, a combustor 16 inwhich the compressed air is mixed with fuel and ignited for generatingan annular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases. The combustor 16 comprisesa combustor wall 20 which is made from sheet metal. It will beunderstood however that the invention is equally applicable to othertypes of gas turbine engines such as a turbo-shaft, a turbo-prop, orauxiliary power units.

Referring to FIG. 2, a number of effusion holes 22 are provided in thecombustor wall 20 and may be drilled at an inclined angle relative to anormal direction of the combustor wall 20. The combustor wall 20surrounds the combustion chamber in which hot combustion gas isproduced. The effusion holes 22 allow pressurized cooling air outside ofthe combustor wall 20 to enter into the combustion chamber and therebycool the combustor 16 by a transpiration or effusion cooling technique.

The number and spacing of the effusion holes 22 (i.e. hole density) canbe determined in accordance with the desired performance characteristicsof the combustor 16. For example, regions of local higher temperature(hot spots) within the combustor may require more cooling than otherregions, and therefore more effusion holes 22 may be required to delivermore cooling air to those specific regions. A hole pattern with suitablehole densities may be selected based on performance or designrequirements and determined using modelling techniques, experimentationor other conventional methods. In the pattern of effusion holes 22 shownin the combustor wall 20 of FIG. 2, a region of lower hole density isshown generally at 28 and a region of higher hole density is showngenerally at 30. The hole pattern comprises a plurality of rows ofspaced holes 22 oriented along a circumferential direction 32 of thecombustor 16 and the rows are spaced apart in an axial direction 34 ofthe combustor 16.

Drilling a large number of holes in parts such as the combustor wall 20according to a relatively complex hole pattern, can be time consuming.High speed laser drilling methods such as drilling-on-the-fly (DOF) arethus preferably used. DOF is described in more detail in U.S.application Ser. No. 11/218,785 filed on Sep. 6, 2005, the contents ofwhich are incorporated herein by reference. During laser drilling, apulsed laser suitable for drilling into the combustor wall 20 is used toproduce each individual hole 22 in the combustor wall 20. While usingthe drilling-on-the-fly (DOF) method, the relative movement between thelaser head and the combustor wall 20 when moving from one hole 22 to thenext is executed between two individual pulses. Accordingly, the shutterdoes not need to be repeatedly closed and opened between each hole. Thisresults in significant time savings.

On a laser drifting system that uses the DOF method, the part to bedrilled is rotated at a constant RPM while the frequency of the laser isset to a constant value. For thinner parts, only one single pulse may berequired to produce each effusion hole 22, and the laser drilling systemmay easily be configured to drill equally spaced holes 22 around anannular combustor wall. Generally three pulses are required to produceeach effusion hole 22 in the combustor wall 20 depending on the systemconfiguration and process conditions.

The task configuring the laser system for drilling effusion holes 22according to a more complex pattern however is more complicated. Inknown techniques, the positional data of every hole 22 in fee patternmust be supplied to the laser drilling system, and the drilling of theeffusion holes 22 is typically done in two stages, wherein a coarserbase hole pattern is first drilled and then one or more finely-spacedholes are drilled between the base holes to produce regions with ahigher hole density.

In accordance with one aspect of the present method, an improved meansof defining a complex effusion hole pattern is possible which results insignificant time savings with respect to the configuration of the laserdrilling system and also the process of drilling the holes 22. Inaccordance with one embodiment, the spacing of the holes 22 along eachrow of holes 22 in the combustor wall 20 is defined using the geometricrelation shown below as equation 1:

L ₁ =aL ₂ =a ² L ₃ =a ³ L ₄ =a ^(n-1) L _(n)=(SR)L _(n)  (1)

where SR is the spacing ratio and is equal to a^(n-1), L₁, L₂ . . .L_(n) are spacing distances between adjacent holes 22 in the row, n isthe number of spaces (i.e. number of holes−1) in the row and a is aconstant. It is evident from equation 1 above that the spaces betweenevery adjacent holes in a row that is defined by equation 1 are relatedto each other. Therefore, in order to determine the position of all theholes in a particular row, only the positional information of one holeserving as an anchor hole, the number of holes in the row, the length ofthe row and the spacing ratio SR must be known. The spacing ratio SR isselected based on a desired hole pattern. The spacing distances (e.g.L₁, L₂ . . . L^(n)) and the value of the constant a are then derivedfrom equation 1.

The spacing ratio SR comprises an exponential function which comprises aconstant base a to the power (n−1). Once a particular hole pattern isdefined based on performance and/or design requirements of the combustor16, the value of the spacing ratio SR is determined by the designer. Thevalue of SR can be chosen such that virtually any hole pattern can berepresented by equation 1. FIG. 3 provides a graphical illustration ofexamples of different hole patterns, shown generally at 36, 38, 40, 42and 44, obtained from the equation when different values of SR areselected. The initial hole for each pattern is shown generally at 46 andthe final hole for each pattern is shown generally at 48.

As seen in pattern 36, for SR> 1, the hole spacing decreasesprogressively from the initial hole 46 to the final hole 48. In pattern38, 0<SR<1 and the hole spacing increases progressively from the initialhole 46 to the final hole 48. For SR=1 a hole pattern 40 is shown havinga uniform hole spacing. In the above cases the SR is defined as thenominal ratio of the last spacing distance to the first spacingdistance.

The use of equation 1 for determining individual spacing distances for ahole pattern defining a hole spacing which decreases progressively fromthe initial hole 46 to the final hole 48 is further illustrated with thenumerical example 1 shown below.

Numerical Example 1 SR>1 Values Provided:

L=5.0″=total length of hole pattern or row of holes

n=5=number of spaces=number of holes−1

SR=2

Determining the Value of Constant a:

a^(n-1)=SR;

a⁵⁻¹=2;

a=1.18921

Determining Spacing Distances:

L=5.0″=L₁+L₂+L₃+L₄+L₅

L₁=a^(n-1)L_(n)=(1.18921)⁴L₅

L₂=a^(n-2)L_(n)=(1.18921)³L₅

L₃=a^(n-3)L_(n)=(1.18921)²L₅

L₄=a^(n-4)L_(n)=(1.18921)¹L₅=(1.18921)L₅

L₅=a^(n-5)L_(n)=(1.18921)⁰L₅=L₃

L=L₅[(1.18921)⁴+(1.18921)³+(1.18921)²+(1.18921)+1]=5.0″

L₅=0.68632″

L₁=1.37265″

L₂=1.1543″

L₃=0.9706″

L₄=0.8162″

Using equation 1, it is also possible to define hole patterns where thespacing gradually decreases or increases from the initial hole 46towards the center of the pattern and then gradually returns to aninitial spacing distance towards the final hole 48. These types of holepatterns are also illustrated in FIG. 3. In these cases, a local holepattern definition is essentially mirrored about the center of theglobal hole pattern that is desired. This technique produces a globalhole pattern that is symmetrical about its center. For the purpose ofdifferentiating this type of hole pattern from a gradually increasing ordecreasing hole pattern, a negative SR can be specified instead of apositive SR. For example, a negative SR can be used to indicate to thehole producing system that the mirroring operation is required. In thecase of a symmetrical hole pattern, the SR is defined as the nominalratio of the center spacing distance to an end (initial or final)spacing distance.

As shown in pattern 40 of FIG. 3, when SR=1 or −1, a uniform holespacing is obtained. In pattern 42, SR<−1 and a denser spacing is foundin the center of the hole pattern 42. Pattern 44 shows the effect of −1<SR< 0 wherein a coarser hole spacing is obtained in the center of thehole pattern 44.

The use of equation 1 for determining individual spacing distances for asymmetrical hole pattern having a hole spacing that is denser at itscenter is further illustrated with the numerical example 2 shown below.

Numerical Example 2 SR<0 Values Provided:

L=5.0″=total length of hole pattern or row of holes (global pattern)

n=5=number of spaces=number of holes−1

SR=−2

Determining Constant a: Consider Half of the Global Pattern forMirroring

n=3=5/2 (rounded to nearest integer)

L=5.0/2=2.5″

a^(n-1)=SR;

a³⁻¹=|−2|;

a=1.4142

Determining Spacing Distances:

L=5.0″=L₁+L₂+L₃+L₄+L₅

L₁=L₅=a^(n-1)L_(n)=a²L₃=(1.4142)²L₃ (mirroring)

L₂=L₄=a^(n-2)L_(n)=aL₃=(1.4142)L₃ (mirroring)

L₃=a^(n-3)L_(n)=(1.4142)⁰L₃=L₃

L=L₃[2(1.4142)²+2(1.4142)+1]=5.0″

L₃=0.6387″

L₁=L₅=(1.4142)²L₃=1.2774″

L₂=L₄=(1.4142)L₃=0.9033″

In order to produce effusion hole patterns which comprise multiple rows,the same equation can also be used to define the axial spacing betweeneach row. The value of L₁ then becomes the first row spacing, the valueof SR is selected based on the desired row spacing and n becomes thenumber of rows in the hole pattern. The length L becomes the distanceacross which the rows are spaced. Positional information of a first rowof holes is also required and may be determined based on the positionalinformation of the first hole in the first row. Therefore the positionalinformation of the first hole (anchor hole) may be used as a referencefrom which the position of individual holes in each row and the positionof each row in the pattern are determined.

The use of such a hole pattern definition results in significant timesavings as positional data for every hole 22 in a row or pattern is notrequired and therefore need not be supplied to the laser-drillingsystem. The position of all the holes 22 in the row are interrelated anddefined by the geometric relation representing the selected hole patterndefinition. Also, all the holes 22 in a row can be drilled sequentiallyusing the DOF method. Typically, effusion holes 22 in a combustor wall20 are drilled using a constant laser pulse frequency with the combustor16 rotating at a constant speed. In order to drill the effusion holes 22sequentially using the geometric relation represented by equation 1, avariable pulse frequency and/or a variable rotating speed may be used.

For a CNC based laser-drilling system, the CNC controller can beconfigured, by implementing a hole pattern definition module through theuse of custom macros and/or subroutines, to accept the necessary inputparameters (position of first hole, number of holes, L and SR) andautomatically determine the position of every hole 22 in the row basedon the geometric relation represented by equation 1. Through the use ofthe hole pattern definition module, the CNC controller can then produceinstructions for the laser drilling system to drill the complete row ofholes 22 sequentially based only on the parameters supplied.

A person skilled, in the art will appreciate that equation 1 is ageneric geometric relation that can be used to represent virtually anyhole pattern desired. However, modifications to equation 1 may be madeor other more specific equations may also be used to representparticular hole patterns. Once a designer has determined a desiredeffusion hole pattern based on performance characteristics orrequirements of the combustor, a specific equation may be determinedusing, for example, curve fitting methods to represent the spacingvalues of the desired hole pattern. For example, in the case of a moresimple effusion hole pattern having spacing values that are linearlydecreasing, the following equation 2 could be used:

Ln=L1−SR(n−1)  (2)

where the spacing ratio SR is a constant value such as 0.1. In thisspecific example, provided a first spacing value L1=1.0, the remainingspacing values would be L2=0.9, L3=0.8 and so forth. Alternatively,specifying a negative SR value in equation 2 would produce a linearlyincreasing effusion hole pattern.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without department from the scope of the invention disclosed.For example, the use of equation 1 is not limited to defining effusionholes 22 to be drilled in walls 20 of combustors 16 for gas turbineengines 10. It is apparent that it can also be used with othercoordinate generation techniques where complex spacing and positions offeatures are represented. For example, a person skilled, in the artwould appreciate that this method of representing spacing patterns canalso be used in conjunction with other manufacturing processes such asconventional milling and drilling, electrical discharge machining (EDM),processes requiring, numerically controlled motion systems and othersimilar processes. Still other modifications which fall within the scopeof the present invention will be apparent to those skilled in the art,in light of a review of this disclosure, and such modifications areintended to fall within the appended claims.

1. A method of producing a plurality of effusion holes in a wall of acombustor of a gas turbine engine, the method comprising the steps of:a) determining a hole pattern definition using: a count of the holes tobe separated by first spaces in a row of holes along a first axis,positional information of a first hole in the row of holes, a firstlength of the row of holes, and, a first spacing ratio relating holespacing distances between each adjacent hole within the row of holes; b)using the hole pattern definition to identify individual positions ofthe effusion holes to be produced in the wall of the combustor; and c)using a hole producing system to produce the effusion holes in the wallof the combustor at the identified positions.
 2. The method as definedin claim 1, wherein the hole pattern definition of step a) is determinedusing the geometric relationL ₁ =aL ₂ =a ² L ₃ =a ³ L ₄ =a ^(n-1) L _(n)=(SR)L _(n), where L₁ is afirst hole spacing distance, a is a constant, n is the number of firstspaces in the row of holes along the first axis, L_(n) is a hole spacingdistance associated with first space number n, and, SR is the firstspacing ratio which is equal to a^(n-1).
 3. The method, as defined inclaim 1, wherein the hole pattern definition of step a) is determined byfurther using: a count of rows of holes to be separated by second spacesalong a second axis; a second length through which the rows of holes arespaced along the second axis; and a second spacing ratio relating rowspacing distances between each adjacent row of holes along the secondaxis.
 4. The method as defined in claim 3, wherein the hole patterndefinition of step a) is determined by further using the geometricrelationL ₁ =aL ₂ =a ² L ₃ =a ³ L ₄ =a ^(n-1) L _(n)=(SR)L _(n), where L₁ is afirst row spacing distance, a is a constant, n is the number of secondspaces along the second axis. La is a row spacing distance associatedwith a second space number n, and, SR is the second spacing ratio whichis equal to a^(n-1).
 5. The method as defined in claim 1, furthercomprising the step of i) designing a desired hole pattern for theeffusion holes based on local hot spots within the combustor, prior tothe determining step a).
 6. The method as defined in claim 5, furthercomprising the step of ii) determining a suitable first spacing ratiobased on the designed hole pattern of step i), prior to the determiningstep a)
 7. The method as defined in claim 3, wherein the first axisrepresents a circumferential direction of the combustor and the secondaxis represents an axial direction of the combustor.
 8. The method asdefined in claim 1, wherein the step of identifying the individualpositions of the effusion holes further comprises mirroring the holepattern.
 9. A method of determining individual positions of effusionholes in a wall of a combustor of a gas turbine engine, the methodcomprising the steps of: a) using a geometric relation that relatesrelative spacing distances between each of the effusion holes separatedby spaces in a row of holes to each other, the geometric relation beingL ₁ =aL ₂ =a ² L ₃ =a ³ L ₄ =a ^(n-1) L _(n)=(SR)L _(n), where L₁ is afirst spacing distance, a is a constant, n is a count of the spaces inthe row of holes, L_(n) is a spacing distance associated with a spacenumber n, and, SR is a spacing ratio which is equal to a^(n-1) andprovides a fractional relationship between spacing distances of anyadjacent hole within the row of holes; and b) using positionalinformation of a first hole in the row of holes, a count of the holesand a length of the row of holes to determine the position of any of theeffusion holes within the row of holes in accordance with the geometricrelation.
 10. The method as defined in claim 9, further comprising thesteps of c) using the geometric relation to relate relative spacingdistances between a plurality of adjacent rows of holes by defining L₁as a first row spacing, n as a count of the rows of holes and selectingSR based on a desired row spacing; and d) using the positionalinformation of a first row of holes, a count of the rows of holes andthe distance across which the rows are spaced to determine the positionof any of the adjacent rows of holes in accordance with the geometricrelation.
 11. The method as defined in claim 10, wherein the positionalinformation of the first row of holes is determined from the positionalinformation of the first hole.
 12. The method as defined in claim 10,wherein the holes in each row of holes are to be spaced along acircumferential direction of the combustor and the rows of holes are tobe spaced along an axial direction of the combustor.
 13. A system forproducing a plurality of spaced holes is a component, the systemcomprising: a hole producing machine; a control system in communicationwith the hole producing machine; a hole pattern definition module whichprovides instructions to the control system for operating andcontrolling the hole producing machine, the hole pattern definitionmodule determining a desired distribution of the effusion holes in thecomponent using predetermined input parameters, the distribution ofeffusion holes being determined in accordance with the geometricrelationL ₁ =aL ₂ =a ² L ₃ =a ³ L ₄ =a ^(n-1) L _(n)=(SR)L _(n), where L₁ is afirst spacing distance, a is a constant, n is a count of the spaces in arow of holes, L_(n) is a spacing distance associated with a space numbern, and, SR is the first spacing ratio which is equal to a^(n-1); thepredetermined input parameters including: a count of the holes to beseparated by spaces in the row of holes along a first axis; positionalinformation of a first hole in the row of holes; a first length of therow of holes; and a first spacing ratio SR relating spacing distancesbetween each adjacent hole within the row of holes.
 14. The system asdefined in claim 13, wherein the hole producing machine comprises alaser drilling machine.
 15. The system as defined in claim 13, whereinthe laser drilling machine is capable of drilling-on-the-fly.